1. Field of the Invention
The present invention relates to a semiconductor light-emitting element and to a method of manufacturing a semiconductor light-emitting element, and in particular relates to technology to improve the efficiency of light extraction of a light-emitting diode (LED).
2. Description of the Related Art
Light-emitting diodes (hereafter abbreviated “LEDs”) are mainly used in the taillights of automobiles, in various display devices, and in the backlights of portable telephones and other mobile equipment. There is anticipated a considerable expansion of demand for its use in the headlights of automobiles, the backlights of liquid crystal displays, and in general lighting fixtures. The light emission efficiency of current LEDs is approximately 50 lm/W. For use in backlights, lighting fixtures and similar, a light emission efficiency of 100 lm/W or higher is necessary. The light emission efficiency of an LED is determined by the product of the internal quantum efficiency when emitting light in the light emission layer and the light extract efficiency for extracting light to the outside The internal quantum efficiency has by now been improved to 80% or higher, but there remains room for improvement of the light extraction efficiency.
One known technology for improving the light extraction efficiency is the provision of roughness in the light emission face of the semiconductor light-emitting element. By making roughness modification in the light emission face, light which is incident at the critical angle or greater at the interface between the semiconductor light-emitting element and the sealing resin and which undergoes total reflection can be reduced. This improves the light extraction efficiency.
This rough shape can be formed by performing appropriate treatment on each light emission face of the semiconductor light-emitting element (p layer surface, growth substrate surface/rear face, and n layer surface after growth substrate separation). For example, Japanese Patent Application Kokai (Laid-open) No. 2006-147787 discloses a semiconductor light-emitting element that has, in order on a sapphire substrate, a low-temperature buffer layer, a first cladding layer, active layer, and second cladding layer. By using the second cladding layer in which growth pits have occurred naturally as a light extraction face, the light extraction efficiency is improved. Alternatively, by performing wet etching or dry etching on the first cladding layer exposed upon separating of the sapphire substrate, bits are formed and therefore the light extraction efficiency is improved.